Musannaf Ibn Abi Shayba 16:893

Abu Bakr narrated to us, he said: Isa bin Yunus narrated to us, from Ibn Jurayj, from Sadaqah bin Yasar, he said: I said to Sa’id bin al-Musayyib, "What should I write on my ring?" He said, "Write on it the remembrance of Allah." And he said: Sa’id commanded me to do that.